Sunday, September 21, 2008

Non-standard tuning is something that has interested me in a long time (I would probably say since early high school). The Sega Mega Drive / Genesis is the perfect candidate for merging my love of chip music with the exploration of non-standard divisions of the octave.

I have added a new feature to the Mega Drive / Genesis MIDI Interface - the ability to tune the pitches of the machine to non 12-TET tuning. 12-TET tuning is a tuning of equal temperament where the octave is divided into twelve logarithmically-equal divisions (semitones), and is the most common scale used in Western music.

The Megadrive can now be tuned to anything from 3-TET (so, the octave is divided three equal parts) to a staggering 128-TET (so, the octave is divided into one hundred and twenty-eight equal parts). This tuning is done via a single MIDI CC message.

The 12-TET is of course the standard tuning when the machine boots up (as one would expect) and the tuning is not entirely perfect (the maximum deviation for a pitch identity across the whole octave is about -0.9 to +0.9 cents).

So of course, the other forms of equally-tempered scales will not be perfectly in tune either. The larger the divisions, the greater the probability of error in comparison to the tuning ratio (of course).

The division process is calculated from MIDI note C-2, so every scale will share the same C-2 MIDI note but will differ more and more as the MIDI note number increases.